A niche opportunity for stem cell therapeutics.

The success of hematopoietic stem cell (HSC)-based therapies relies on the ability of the stem cells to both engraft and self-renew sufficiently in the bone marrow microenvironment. Previous studies identified that a number of components of bone contribute to the regulation of HSCs indicating that they participate in a stem cell 'niche'. This niche is a dynamic microenvironment that changes during development and with varying physiologic states. Components of it, such as the osteoblast, can be modulated through pharmacological treatment. Reasoning that the stem cell niche may be manipulated to augment the effectiveness of stem cell therapies, we demonstrated that daily treatment with parathyroid hormone (a clinically approved method for increasing osteoblast function) resulted in therapeutic benefit in three clinically relevant models of stem cell therapy. These results suggest that the niche may be a pharmacological target for altering stem cell function in settings of regenerative medicine.